The department is named after river Ain (200 km), tributary of the Rhône.
The creation of the Lyon Intermunicipal Authority has caused the transfer (Law of 29 December 1967, published in the French official gazette on 30 December 1967, with effect on 31 December 1967) of the six municipalities of Genay, Montanay, Rillieux, Crépieux-la-Pape (merged in 1972 with Rillieux to form Rillieux-la-Pape), Sathonay-Camp and Sathonay-Village from the department of Ain to the department of Rhône (map). Accordingly, Ain lost 37 km2 of its territory.

Ivan Sache, 11 November 2009

Flag of Ain

The flags representing the departments of Region Rhône-Alpes are
hoisted, together with the Region's flag, in front of the seat of the
Regional Council at Charbonnières-les-Bains, near Lyon (photo, 12 February 2006).
The Department of Ain is represented by a banner of arms:
"Quarterly: 1. Or a bend azure between two lions rampant sable; 2.
Azure three hempbrakes fesswise in pale or tied argent a chief argent
a demi-lion rampant issuant gules; 3. Azure three fleurs de lis or
overall a bendlet couped gules; 4. Gules a lion rampant ermine."
There is no evidence, however, of the use of this flag in the
Department of Ain.

Paul Chaix (Armorial des communes et collectivités des pays de
l'Ain, 1995) gives a different coat of arms (description) for the Department, with the first quarter, "Azure a lion rampant contourned ermine" and in the cross botonny argent placed overall.
These arms are intended to represent the four traditional components
of the department, 1. Pays of Bresse, as the arms of the lords of
Bâgé-le-Châtel, the fomer capital of Bresse; 2. Pays de Gex, as the arms of the Joinville family; 3. Dombes, as the arms of Bourbon, owners of Dombes since 1400. 4. Bugey, as the arms of the local lords.
The cross bottony, from the arms of the Order of St. Maurice, is taken
from the arms of Bourg-en-Bresse, the capital of the department.

The main discrepancy between the flag and the arms of Ain, except the
cross not shown on the flag, is the first quarter representing Bresse.
According to Brian Timms, Robert Louis assigned to Ain the former arms of Bresse, "Argent a bend azure between two lions rampant sable". These arms were indeed ascribed to Bresse in the Armorial Général. The flag of Ain uses the same arms in its first quarter, but with the field yellow instead of white.
For Pays de Gex, Timms recalls that the Joinville (same family as the
famous chronicler Jean de Joinville, 1225-1317) were lords of Gex in
1251-1353. The hempbrakes are shown in the municipal arms of Joinville
(Department of Haute-Marne, Region Champagne) as the canting arms (in usual French, a hempbrake is called broie) of the Broyes family, a cadet of Joinville.